(1) Field of the Invention
The present invention relates to a tandem type color image forming apparatus and its control method wherein a multiple number of image forming devices for forming different colors of images are placed serially in the direction of conveyance of recording media. The present invention is particularly directed to a tandem type color image forming apparatus and its control method wherein different image forming modes are used for monochrome and multi-color image forming operations.
(2) Description of the Prior Art
Conventionally there have been known tandem type color image forming apparatuses, which are improved in throughput of image forming by serially arranging multiple, e.g., four image stations (image forming units or image forming devices) having image supports forming electrostatic latent images corresponding to multiple colors, e.g., four image colors K: black, C: cyan, M: magenta and Y: yellow, along the direction of conveyance of recording media.
In such a conventional tandem type color image forming apparatus, usually there is use of only one image forming station, with the others unused, when a monochrome image is formed. Therefore, in the monochrome image forming mode, the image supports of the image forming stations other than the one needed are adapted to stop rotating.
Since the image supports are stopped rotating by the above arrangement so that the image supports will not come into contact with the recording media, an intermediate transfer medium, or the like, more than needed, it is possible to avoid deterioration of the image supports due to abrasion and the like. Thus, this control leads to reduction in running cost.
In particular, in color image forming apparatuses, use of B/W (monochrome) image forming is made more frequently compared to use of full and mono color image forming operations. Therefore, the image forming stations other than that for K, or more explicitly, for C, M and Y are, in most cases, kept away from the recording media or the intermediate medium.
In this case, upon a mode change between monochrome image forming and color image forming, image supports to be non-rotated are separated from the transfer belt as a transfer support or image supports to be rotated are set into contact therewith. Therefore, with conventional typical technologies, the image supports are adapted to start rotating after discharge of the recording sheet from the transfer belt. Then, the image supports are shifted or the transfer belt or the transfer and conveyance support for supporting a transfer belt is shifted so that the supports to be rotated come into contact with the transfer belt while the image supports are stopped rotating after the transfer belt or the transfer and conveyance support for supporting a transfer belt is shifted so that the supports to be non-rotated are moved away from the transfer belt.
However, since the operation relating to the-separation and abutment of the image supports and the transfer belt needs a certain period of time, there has been a problem that it takes along time if a set of documents which contains monochrome pages without color images and multicolor pages with color images needs to be image formed.
In order to solve the above problem, a variety of technologies have been proposed.
For example, Japanese Patent Application Laid-open Hei 11 No. 133697 discloses a technology in which a rearrangement control means is provided in order to change the order of pages to be formed with images where the pages containing color and monochrome images are segregated into color page and monochrome page groups and reproduced separately one from the other. In this prior art, since it is possible to reduce the number times the transfer and conveyance support is shifted, it is not only possible to reduce the running cost but also to solve the above problem, or reduce the time for image forming of the whole images.
However, even though the method disclosed in Japanese Patent Application Laid-open Hei 11 No. 133697 is able to reduce the time for image forming, it entails new problems including increase in cost and lowering of user convenience.
More specifically, provision of the rearrangement control means increases the complexity of the control system of the color image forming apparatus hence increase the production cost of the machine and the cost for maintenance. Further, since the recording sheets with images formed using the rearrangement control means are not arranged in the correct order, the user has to rearrange them in the collated order.
In this case, an intermediate tray or the like which can temporarily hold the recording sheets may be provided in the color image forming apparatus so that the recording sheets printed out first and the recording sheets printed out later can be rearranged in the collated order. However, provision of the intermediate tray increases the number of parts of the color image forming apparatus and hence further increases the production cost, which results in an inefficient solution.
The present invention has been devised in view of the above problems, it is therefore an object of the present invention to provide a color image forming apparatus and its control method, wherein, when documents which include monochrome pages without color images and multicolor pages with color images are handled for image forming, the speed of image forming can be improved without any change of printed page order while degradation of the image supports can be prevented.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a color image forming apparatus includes: a plurality of image forming devices placed serially in the direction of conveyance of recording sheets; a transfer support which is arranged in abutment with image supports provided in the image forming devices and is separable therefrom, for transferring images from the image supports to a recording sheet; a mode switching means for making a changeover between the monochrome image forming mode for forming images using only one image forming device of the plural image forming devices and the multi-color image forming mode for forming images using the plural image forming devices; and a control means for governing the image forming devices, the image supports, the transfer support and the mode switching means, the control means making a control so that the transfer support can abut only the image forming devices which are actually engaged in image forming, among the plural image forming devices, and is characterized in that the mode switching means starts the changeover from the monochrome image forming mode to the multi-color image forming mode while the recording sheet remains on the transfer support.
In accordance with the second aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the mode switching means starts the mode change immediately after the image has been transferred from the image support of the most upstream image forming device to the recording sheet.
In accordance with the third aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that each of the image supports is comprised of a rotational photoreceptor drum and the control means makes a control so that the transfer support abuts the image supports after the image supports start rotating.
In accordance with the fourth aspect of the present invention, the color image forming apparatus having the above second feature is characterized in that each of the image supports is comprised of a rotational photoreceptor drum and the control means makes a control so that the transfer support abuts the image supports after the image supports start rotating.
In accordance with the fifth aspect of the present invention, the color image forming apparatus having the above third feature is characterized in that at least the surface of the transfer support moves in the direction of conveyance of the recording sheet and the control means makes a control so that the image supports and transfer support abut each other after the rotational speeds of the image supports and that of the transfer support coincide.
In accordance with the sixth aspect of the present invention, the color image forming apparatus having the above fourth feature is characterized in that at least the surface of the transfer support moves in the direction of conveyance of the recording sheet and the control means makes a control so that the image supports and transfer support abut each other after the rotational speeds of the image supports and that of the transfer support coincide.
In accordance with the seventh aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the eighth aspect of the present invention, the color image forming apparatus having the above seventh feature further comprises a control means for setting the initial mode at the activation of the power supply and at the ready mode, into either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the ninth aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the transfer support is comprised of a transfer and conveyance support for conveying the recording sheet by its rotationally moving surface or an intermediate transfer support to which images are transferred from the image supports.
In accordance with the tenth aspect of the present invention, the color image forming apparatus having the above first feature further comprises a shifting means for shifting the image supports and/or the transfer support.
In accordance with the eleventh aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that, upon a mode change from the monochrome image forming mode to the multi-color image forming mode, the transfer support is caused to abut the plural image forming devices used for the multi-color image forming mode, after when the rear end of the recording sheet having passed through the transfer station of the image forming device used for the monochrome image forming mode, has passed through the most upstream image forming device of those used in the multi-color image forming mode.
In accordance with the twelfth aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the transfer support conveys the recording sheet at a speed higher than the speed of conveyance of the recording sheet at the image forming device used in the monochrome image forming mode, during the period from when the rear end of the recording sheet has passed through the image forming device used for the monochrome image forming mode until it passes through at least the most upstream image forming device among those used in the multi-color mode.
In accordance with the thirteenth aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that printing at a mode change from the monochrome image forming mode to the multi-color image forming mode starts after at least one of the image forming devices used for the multi-color image forming mode has become abutted with the transfer support.
In accordance with the fourteenth aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that, upon a mode change from the monochrome image forming mode to the multi-color image forming mode, the speed of conveyance of the recording sheet on the transfer support is increased to be greater than the speed of conveyance of the recording sheet passing at the image forming device used in the monochrome image forming mode, and during this period, the image forming devices for the monochrome image forming mode and the multi-color image forming mode, abutting the transfer support, are rotated at a peripheral speed equal to or greater than the speed at which the recording sheet is conveyed by the transfer support.
In accordance with the fifteenth aspect of the present invention, the color image forming apparatus having the above fourteenth feature is characterized in that the peripheral speeds of the image forming devices used in the monochrome image forming mode and in the multi-color image forming mode are set to fall within the range of 1.0 to 1.2 times of the speed at which the recording sheet is conveyed by the transfer support.
In accordance with the sixteenth aspect of the present invention, the color image forming apparatus having the above fourteenth feature is characterized in that the status in which the rotational speed of the image forming devices used in the multi-color image forming mode is greater than the speed of conveyance of the recording sheet on the transfer support is made to end after the rear end of the recording sheet has passed through the most downstream image forming device adjacent to the fixing mechanism to be located next to the transfer support and the rotational speed of the image forming devices is shifted into the speed for the multi-color image forming mode.
In accordance with the seventeenth aspect of the present invention, the color image forming apparatus having the above twelfth feature is characterized in that the speed of conveyance of the recording sheet by the transfer support is increased to be greater than the speed of conveyance of the recording sheet passing at the image forming device used in the monochrome image forming mode, and during this period, a higher voltage than the erasing voltage that is applied at the normal speed is applied to a transfer support erasing element arranged with the transfer support.
In accordance with the eighteenth aspect of the present invention, the color image forming apparatus having the above fourteenth feature is characterized in that a higher voltage than the erasing voltage that is applied at the normal speed is applied to the erasing elements of the image forming devices used in the monochrome image forming mode and the multi-color image forming mode, during the period in which the rotational speed of the image forming devices used in the monochrome image forming mode and the multi-color image forming mode is set to be equal to or greater than the speed of conveyance of the recording sheet on the transfer support.
In accordance with the nineteenth aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the rotational speed of the plural image forming devices is kept to be equal to or greater than the speed of conveyance of the recording sheet on the transfer support until the leading end of the recording sheet is conveyed to the fixing mechanism which is located downstream of the transfer support.
In accordance with the twentieth aspect of the present invention, the color image forming apparatus having the above nineteenth feature is characterized in that, upon a mode change from the monochrome image forming mode to the multi-color image forming mode, the speed at which the recording sheet is conveyed through the fixing mechanism is kept constant from the leading end of the recording sheet reaches the fixing mechanism until the rear end of the recording sheet passes through the fixing mechanism.
In accordance with the twenty-first aspect of the present invention, a control method of a color image forming apparatus which comprises: a plurality of image forming devices placed serially in the direction of conveyance of recording sheets; and a transfer support arranged in abutment with each image support provided in each image forming device, in a separable manner therefrom, and is controlled so that the transfer support is separated from the image supports when a plurality of image forming devices are not used for image forming, wherein the operating mode can be changed over between the monochrome image forming mode for forming images using only one image forming device of the plural image forming devices and the multi-color image forming mode for forming images using the plurality of image forming devices, is characterized in that the mode change from the monochrome image forming mode to the multi-color image forming mode is started while the recording sheet remains on the transfer support.
In accordance with the twenty-second aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-first feature is characterized in that the action of the image forming mode change is started immediately after the image formed on the image support of the most upstream image forming device has transferred to the recording sheet.
In accordance with the twenty-third aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-first feature is characterized in that the image supports and the transfer support are both configured to be rotatable and the transfer support is caused to abut the image supports after the image supports have started rotating.
In accordance with the twenty-fourth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-second feature is characterized in that the image supports and the transfer support are both configured to be rotatable and the transfer support is caused to abut the image supports after the image supports have started rotating.
In accordance with the twenty-fifth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-third feature is characterized in that the image supports and the transfer support are made to abut each other after the rotational speeds of the image supports and that of the transfer support at the abutment portions coincide.
In accordance with the twenty-sixth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-fourth feature is characterized in that the image supports and the transfer support are made to abut each other after the rotational speeds of the image supports and that of the transfer support at the abutment portions coincide.
In accordance with the twenty-seventh aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-first feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the twenty-eighth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-second feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the twenty-nine aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-third feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the thirtieth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-fourth feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the thirty-first aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-fifth feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the thirty-second aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-sixth feature is characterized in that the initial mode when the power supply is turned on and in the ready mode can be set at either the monochrome image forming mode or the multi-color image forming mode.
In accordance with the thirty-third aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-seventh feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.
In accordance with the thirty-fourth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-eighth feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.
In accordance with the thirty-fifth aspect of the present invention, the control method of a color image forming apparatus, having the above twenty-ninth feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.
In accordance with the thirty-sixth aspect of the present invention, the control method of a color image forming apparatus, having the above thirtieth feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.
In accordance with the thirty-seventh aspect of the present invention, the control method of a color image forming apparatus, having the above thirty-first feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.
In accordance with the thirty-eighth aspect of the present invention, the control method of a color image forming apparatus, having the above thirty-second feature is characterized in that the initial mode is set to be either the monochrome image forming mode or the multi-color image forming mode by the predetermined operation through a control means.